Go to www.reserveamerica.com
. On that website you can do a general search. Under "Find Campgrounds" just tell it what kind of campsite you want and then put in the name of a town near where you want to camp. Then put in the date range you want, the number of nights you want to stay and hit the "Search Campgrounds" button.
It will return a list of campgrounds that meet your criteria (and are in the Reserve America System). You will get state parks, corp of engineers (listed as Federal) and private campgrounds. Each one will list the distance, in miles, from the town you said you wanted to be near.
It is a pretty good tool for casting a wide net for campgrounds that might be what you need during the time you want.
Just for grins I went specifically to Inks lake just to see how booked up they were. We have stayed there and I know you need to plan ahead but I was shocked to find that there were no 5 consecutive nights available through March of 2009!
I then did the search as I described above and found 45 possible alternatives. Granted, some were 195 miles away, but they were available.